Examples of image processing apparatus include a facsimile machine. A facsimile machine needs to have both an image reading function and an image printing function. Further, it is desired that a facsimile machine is so structured to have a size as small as possible.
Therefore, a prior art image read/write head H has the structure as shown in FIG. 15. The image read/write head H includes a case 1e and a transparent cover 19e mounted on an upper portion of the case. The head case 1e accommodates light sources 30e for illuminating an image reading line Se defined on a surface of the transparent cover 19e, and lenses 5e. A substrate 4e is mounted at the bottom of the case 1e. The substrate 4e has an obverse surface 40 and a reverse surface 41 respectively provided with a plurality of light receiving elements 3e and a plurality of heating elements 8e in respective rows extending longitudinally of the substrate 4e. On the reverse surface 41 of the substrate 4e are also mounted a plurality of drive IC chips 80e incorporating driving circuits for providing drive control of the heating elements 8e. 
With such an image read/write head H, a document D is transferred by a platen roller P1 in close contact with the obverse surface of the transparent cover 19e. During the transferring step, a surface of the document D is illuminated by the light sources 30e. The light reflected by the document D is collected by the lenses 5e, thereby forming an image of the document D on the light receiving elements 3e, which output image signals. On the other hand, a recording paper K of heat-sensitive type is transferred by a platen roller P2 in close contact with the heating elements 8e. During the transferring step, the driving circuits in the drive IC chips 80e drive selected ones of the heating elements 8e for heat generation. As a result, an image is printed on the recording paper K. The facsimile machine incorporating the image read/write head H can be made smaller in thickness than a facsimile machine in which a reading head and a printing head are separately provided.
However, the above-described prior art structure has the following problems.
Firstly, as described above, the image read/write head H is used in combination with a pair of platen rollers P1 and P2 for a document and a recording paper, respectively. Therefore, it is desired that the image read/write head H has such a structure as to allow easy positioning and mounting of the platen rollers P1 and P2 relative to the image read/write head. However, the prior art image read/write head H does not include such positioning or mounting means, which is inconvenient.
Secondly, the platen rollers P1, P2 are disposed so as to sandwich the image read/write head H, so that the image read/write head H in combination with the platen rollers P1 and P2 becomes bulky in the thickness direction of the image read/write head.
Thirdly, in manufacturing the image read/write head H, after a plurality of light receiving elements 3e are mounted on an obverse surface 40 of a substrate 4, the substrate needs to be turned over for mounting a plurality of heating elements 8 and a plurality of drive IC chips 80 on a reverse surface 41 of the substrate 4. Moreover, wiring patterns with respect to these components also need to be provided on both the obverse and the reverse surfaces 40, 41 of the substrate 4. Therefore, the image read/write head H cannot be efficiently manufactured.
Fourthly, there is a likelihood that the light receiving elements 3e receive inappropriate light which may cause noises. Specifically, with the above-described prior art structure, the light passing through the lenses 5e may be reflected in a scattering manner by the wall surfaces around the light receiving elements 3e, and the scattering light may be received by the light receiving elements 3e. Moreover, light from outside the case 1e may enter the case 1e through a small gap defined between the case 1e and the substrate 4e to be received by the light receiving elements 3e. 
Fifthly, with the prior art image read/write head H, it is impossible to determine whether or not the document D is fed onto the transparent cover 19e. Similarly, it is also impossible to determine whether or not the recording paper K is fed on the heating elements 8. Therefore, as indicated by phantom lines in FIG. 15, sensors 99a, 99b for detecting the presence or absence of the document D and the recording paper K, respectively, need to be provided separately from the image read/write head H. With such an arrangement, the sensors 99a, 99b and the image read/write head H need to be individually mounted at respective positions, which makes the manufacturing process of an image processing apparatus troublesome. Further, the image reading operation may be controlled to be interrupted when the document D is advanced by a predetermined distance after the trailing edge of the document D is detected by the sensor 99a. In such a case, it is necessary to precisely set the distance between the sensor 99a and the image reading line Se of the image read/write head H, which is also troublesome.